1. Field of the Invention
This invention relates to electrolytic removal of metal from solutions, and has particular reference to the recovery of silver from exhausted photographic film processing solutions by an electrolytic process wherein an electric current is passed between anode and cathode electrodes immersed in the solution to cause the silver to be removed from the solution and deposited on the cathode.
2. Discussion of the Prior Art
It is common practice to recover silver from exhausted photographic processing solutions. The greatest amount of silver is recovered from photographic fixing solutions which contain either sodium thiosulfate or ammonium thiosulfate, and most of the prior art silver recovery systems of the electrolytic type employ means to continuously rotate or otherwise move the cathode through the solution at a rapid rate to reduce the concentration of sodium ions so that they will not cause decomposition of the thiosulfate, which decomposition would cause the formation of unwanted silver sulfide.
Although such prior systems are generally satisfactory, the silver does not always build up evenly over the surface of the cathode, and this results in an unbalanced condition which tends to cause wobbling or vibration as the cathode is rotated. Also, as the recovered silver builds up on the cathode, the loading on its bearings increases. Moreover, after a certain amount of silver has been built up, it must be stripped from the cathode by chipping, or otherwise cutting the same, so that the cathode may be re-used. This is tedious and time-consuming.
Attempts have been made to overcome the above problems by rotating the anode and maintaining the cathode stationary. However, in those systems of which applicants are aware, the cathode or cathodes are in the form of solid bars or plates, from which the silver must be stripped.
In addition, prior silver recovery systems generally require considerable dismantling in order to periodically remove the silver from the cathode. This is not only time-consuming, but during the dismantling there is a tendency for some of the corrosive and stain-producing solution to splash or spill onto the floor and other surrounding areas.